linux-kernel - Re: [x86] Unify semaphore_32.S and rwlock

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Date:	Wed, 20 Jan 2010 16:46:29 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Christoph Lameter <cl@...ux-foundation.org>
cc:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org, Andi Kleen <andi@...stfloor.org>
Subject: Re: [x86] Unify semaphore_32.S and rwlock_64.S

On Wed, 20 Jan 2010, Linus Torvalds wrote:
> 
> 	#define RWSEM_UNLOCKED_VALUE            0x00000000
> 	#define RWSEM_ACTIVE_BIAS               0x00000001
> 	#define RWSEM_ACTIVE_MASK               0x3fffffff
> 	#define RWSEM_WAITING_BIAS              (~RWSEM_ACTIVE_MASK)
> 	#define RWSEM_ACTIVE_READ_BIAS          RWSEM_ACTIVE_BIAS
> 	#define RWSEM_ACTIVE_WRITE_BIAS         (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)

Btw, doing that RWSEM_WAITING_BIAS cleanup (we currently have it as an 
independent constant) means that now all constants are shared except for 
that RWSEM_ACTIVE_MASK. So it ends up being something like this:

	#ifdef CONFIG_RWSEM_64bit
	  typedef __s64 rwsem_count_t;
	  #define RWSEM_ACTIVE_MASK	0x3fffffff
	#else
	  typedef __s32 rwsem_count_t;
	  #define RWSEM_ACTIVE_MASK     0xffff
	#endif

	#define RWSEM_UNLOCKED_VALUE	0x00000000
	#define RWSEM_ACTIVE_BIAS	0x00000001
	#define RWSEM_WAITING_BIAS	(~RWSEM_ACTIVE_MASK)
	#define RWSEM_ACTIVE_READ_BIAS	RWSEM_ACTIVE_BIAS   
	#define RWSEM_ACTIVE_WRITE_BIAS	(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)

with just that two-line difference for the 32-bit/64-bit case.

At least I _think_ so.

And it's worth noting (again) that I didn't actually push the 
twsem_count_t changes down into the slow-path code in lib/rwsem.c. There's 
a few variables there that might need looking at too. I _think_ they are 
all ok as-is (unlike the header file, lib/rwsem.c seems to consistently 
use 'signed long' rather than mix 32-bit and 64-bit types), but it migh be 
cleaner to make them rwsem_count_t's too.

			Linus
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